1. Field of the Invention
The present invention relates to a camera, such as a digital camera, a digital video camera or a camera-equipped mobile phone, which generates a timing signal for driving an image-capturing element and reads out a pixel signal, and a timing signal processing apparatus which generates a timing signal for use in the camera.
2. Description of the Related Art
In recent years, with an increase in the number of pixels in cameras such as digital cameras, there is a tendency for higher power to be needed to drive an image-capturing element such as a charge-coupled device (COD). In addition, with the provision of various functions such as an anti-shake function (correction of image distortion due to shaking of the hand), there is a tendency for the power consumption of the entire camera to increase. In contrast, in consideration of the convenience for users, there is a demand for longer battery life, that is, lower power consumption.
In the prior art, there has been proposed a camera which can reduce power consumption in the case where a CCD with a great number of pixels is used (see, e.g. Jpn. Pat. Appln. KOKAI Publication No. 2003-60994).
In the prior-art camera, the power consumption is reduced by switching the driving frequency of a driving pulse, which is supplied from a timing signal generating circuit to the CCD, between a first frequency, which is generated on the basis of a clock that is supplied from a clock generating circuit, and a second frequency which is higher than the first frequency, in accordance with a read mode which is selected from a plurality of read modes.
However, in some types of CCDs, a driving frequency, which is set by specifications, needs to be used for stable operations. Even in cases where the driving frequency is variable, the operation may become unstable when the driving frequency is dynamically varied.
When the driving frequency for the CCD is lowered, the transfer time of a charge (pixel signal) from a light-receiving element (photodiode) of the CCD increases. For example, if intense light is incident, leakage of charge from the light-receiving element to a vertical CCD occurs and mixes in the read charge. That is, smear occurs. As the read time becomes longer, the leakage of charge becomes greater. Thus, if the driving frequency is lowered and the read time is increased as in the prior art, the image quality may deteriorate.